DRAM interconnect structure having ferroelectric capacitors exhibiting negative capacitance

ABSTRACT

An interconnect structure for use in coupling transistors in an integrated circuit is disclosed, including various configurations in which ferroelectric capacitors exhibiting negative capacitance are coupled in series with dielectric capacitors. In one embodiment, the negative capacitor includes a dielectric/ferroelectric bi-layer. When a negative capacitor is electrically coupled in series with a conventional dielectric capacitor, the series combination behaves like a stable ferroelectric capacitor for which the overall capacitance can be measured experimentally, and tuned to a desired value. The composite capacitance of a dielectric capacitor and a ferroelectric capacitor having negative capacitance coupled in series is, in theory, infinite, and in practice, very large. A series combination of positive and negative capacitors within a microelectronic interconnect structure can be used to make high capacity DRAM memory cells.

BACKGROUND

Technical Field

The present disclosure generally relates to high speed integratedcircuits, and in particular, to the use of ferroelectric capacitors toimprove performance of DRAM memory cells.

Description of the Related Art

Transistor devices are coupled together by multi-layer metalinterconnect structures to form integrated circuits (ICs) such as logicdevices, or processors, and random access memory arrays such as staticRAM (SRAM), dynamic RAM (DRAM), and flash memory. As the dimensions ofintegrated circuit elements continue to shrink below 20 nm, integrationof new materials within the interconnect structures becomes morechallenging. Materials used to form the interconnect structure at the 20nm technology node include various metals and ultra-low-k (ULK)dielectrics that provide insulation between stacked metal layers, andbetween adjacent metal lines. To achieve fast device operation, it isimportant that vertical capacitances between the metal layers andhorizontal capacitances between the metal lines are minimized. While itis desirable to reduce the vertical capacitances as much as possible byusing ULK dielectrics, such materials tend to be porous and lackstructural integrity, as is described in U.S. patent application Ser.Nos. 14/098,286 and 14/098,346 to the same inventor as the inventor ofthis patent application. While device speeds benefit from smallcapacitances, DRAMs and other high speed, high density memories underdevelopment require larger capacitances for increased storage capacity,and low power operation. Thus a conflict arises, for memory ICs inparticular, between the need for higher speed and larger storagecapacity.

As is well known in the art, conventional dielectric capacitors includetwo conducting plates separated by a dielectric material such as, forexample, silicon dioxide (SiO₂). When a voltage is applied across theplates, dipole moments within the dielectric material align to producean internal polarization P that opposes the electric field E associatedwith the applied voltage, thus allowing positive charge to remain on onemetal plate and negative charge to remain on the other conducting plate,as stored charge. The amount of charge stored on the plates isproportional to the applied voltage, according to the linearrelationship Q=CV. The constant of proportionality, C, is known ascapacitance, which is a positive value. A conventional capacitor has afixed capacitance that is independent of the circuit in which it isused. Furthermore, the relationship between the polarization P and theapplied electric field E is also linear.

There also exist ferroelectric capacitors in which a ferroelectricmaterial is substituted for the dielectric material between theconducting plates. Behavior of ferroelectric capacitors for use innanoscale devices is described by Salahuddin and Datta (Nano Letters,Vol. 8, No. 2, pp. 405-410). At certain temperatures, ferroelectricmaterials exhibit spontaneous polarization P that can be reversed byapplying an electric field. Materials that have ferroelectric propertiesat, or close to, room temperature include, for example, barium titanate(BaTiO₃), lead titanate (PbTiO₃), and lead zirconate titanate (PZT). Inanalogy with ferromagnetic materials, the relationship between thepolarization P and the applied electric field E of a ferroelectriccapacitor exhibits hysteresis and is therefore non-linear. Furthermore,there can be a region of the associated hysteresis curve in which theslope dP/dE is negative and the capacitor is unstable. Normally, theinduced polarization opposes the applied electric field. However, duringan intermittent time interval during which the slope of the hysteresiscurve is negative, the induced polarization enhances the applied field,thus creating positive feedback.

Because the ferroelectric material is already polarized before a voltageis even applied, the charge stored in the ferroelectric capacitor is notzero when V=0. Instead, the relationship between the stored charge andthe capacitance is given byQ=C _(o)(V+αQ).  (1)In Equation (1) αQ is a feedback voltage that is proportional to thecharge Q on the capacitor, wherein a is α constant of proportionality.The effective capacitance C_(eff) that satisfies the relationshipQ=C_(eff)V is then given by C_(eff)=C_(o)/(1−αC_(o)), whichtheoretically can be a negative number when α C_(o)>1. Negative valuesof C_(eff) are associated with the unstable region of the hysteresiscurve and are unlikely to be observed experimentally.

BRIEF SUMMARY

When a ferroelectric capacitor having a negative effective capacitanceis electrically coupled in series with a conventional dielectriccapacitor, the series combination behaves like a stable ferroelectriccapacitor. In other words, the series configuration has a stabilizingeffect on the negative capacitor, such that the overall capacitance canbe measured experimentally, and tuned to a desired value. It is wellknown that connecting two identical conventional dielectric capacitorsin series lowers the overall capacitance by half:C _(tot)=[1/C ₁+1/C ₁]⁻¹ =C ₁/2.  (2)Thus, by forming positive capacitors in series within a transistorinterconnect structure, the need for reduced interconnect capacitance issatisfied. Applying equation (2) to determine the overall, or composite,capacitance of a dielectric capacitor C₁ and a ferroelectric capacitor−C₁ coupled in series yieldsC _(tot)=[1/C ₁+1/(−C ₁)]⁻¹=0⁻¹=∞.  (3)

While an infinite capacitance is not realistic, equation (3) predicts avery large value for a series combination of positive and negativecapacitors. Thus, by forming positive and negative capacitors in serieswithin the interconnect structure, high capacity DRAM memory cells arealso provided.

Based on these predictions, an interconnect structure for use incoupling transistors in an integrated circuit is presented herein,including various configurations in which ferroelectric capacitorsexhibiting negative capacitance are coupled in series with dielectriccapacitors. In one embodiment, the ferroelectric capacitors include adielectric/ferroelectric bi-layer.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the drawings, identical reference numbers identify similar elements.The sizes and relative positions of elements in the drawings are notnecessarily drawn to scale.

FIG. 1A is a circuit schematic of a conventional dynamic random accessmemory (DRAM) cell, according to the prior art.

FIG. 1B is a cross-sectional view of a conventional DRAM cell shown inFIG. 1A, according to the prior art.

FIG. 2A is a pictorial perspective view of a prior artdielectric/ferroelectric bi-layer.

FIG. 2B is a circuit schematic of the dielectric/ferroelectric bi-layershown in FIG. 2A.

FIG. 2C is a plot of polarization as a function of applied electricfield for a prior art ferroelectric capacitor exhibiting negativecapacitance.

FIG. 3A is a plot of capacitance for a single layer prior art PZTferroelectric capacitor, in response to an applied current pulse.

FIG. 3B is a plot of capacitance for a prior art series combination of aferroelectric capacitor and a dielectric capacitor, in response to anapplied current pulse.

FIG. 3C is a family of plots of inverse capacitance as a function ofdielectric thickness showing positive capacitance for a prior artdielectric capacitor and negative capacitance for a prior artferroelectric capacitor.

FIG. 4 is a pictorial view of a pair of ferroelectric DRAM cellsaccording to the prior art.

FIG. 5 is a cross-sectional view of a pair of capacitive structures foruse in integrated circuit ferroelectric DRAM cells, according to oneembodiment described herein.

FIG. 6 is a flow diagram showing generalized steps in a method offabricating an array of ferroelectric capacitive cells, as describedherein.

FIG. 7 is a cross-sectional view of a positive capacitor array,according to one embodiment described herein.

FIG. 8 is a cross-sectional view of a negative capacitor array,according to one embodiment described herein.

FIG. 9 is a cross-sectional view of a completed array of ferroelectriccapacitive cells, according to a first embodiment described herein.

FIG. 10 is a cross-sectional view of a completed array of ferroelectriccapacitive cells, according to a second embodiment described herein.

FIG. 11 is a cross-sectional view of a completed array of ferroelectriccapacitive cells, according to a third embodiment described herein.

DETAILED DESCRIPTION

In the following description, certain specific details are set forth inorder to provide a thorough understanding of various aspects of thedisclosed subject matter. However, the disclosed subject matter may bepracticed without these specific details. In some instances, well-knownstructures and methods of semiconductor processing comprisingembodiments of the subject matter disclosed herein have not beendescribed in detail to avoid obscuring the descriptions of other aspectsof the present disclosure.

Unless the context requires otherwise, throughout the specification andclaims that follow, the word “comprise” and variations thereof, such as“comprises” and “comprising” are to be construed in an open, inclusivesense, that is, as “including, but not limited to.”

Reference throughout the specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment. Thus, the appearance of the phrases “in oneembodiment” or “in an embodiment” in various places throughout thespecification are not necessarily all referring to the same aspect.Furthermore, the particular features, structures, or characteristics maybe combined in any suitable manner in one or more aspects of the presentdisclosure.

Reference throughout the specification to integrated circuits isgenerally intended to include integrated circuit components built onsemiconducting substrates, whether or not the components are coupledtogether into a circuit or able to be interconnected. Throughout thespecification, the term “layer” is used in its broadest sense to includea thin film, a cap, or the like and one layer may be composed ofmultiple sub-layers.

Reference throughout the specification to conventional thin filmdeposition techniques for depositing silicon nitride, silicon dioxide,metals, or similar materials include such processes as chemical vapordeposition (CVD), low-pressure chemical vapor deposition (LPCVD), metalorganic chemical vapor deposition (MOCVD), plasma-enhanced chemicalvapor deposition (PECVD), plasma vapor deposition (PVD), atomic layerdeposition (ALD), molecular beam epitaxy (MBE), electroplating,electro-less plating, and the like. Specific embodiments are describedherein with reference to examples of such processes. However, thepresent disclosure and the reference to certain deposition techniquesshould not be limited to those described. For example, in somecircumstances, a description that references CVD may alternatively bedone using PVD, or a description that specifies electroplating mayalternatively be accomplished using electro-less plating. Furthermore,reference to conventional techniques of thin film formation may includegrowing a film in-situ. For example, in some embodiments, controlledgrowth of an oxide to a desired thickness can be achieved by exposing asilicon surface to oxygen gas or to moisture in a heated chamber.

Reference throughout the specification to conventional photolithographytechniques, known in the art of semiconductor fabrication for patterningvarious thin films, includes a spin-expose-develop process sequencetypically followed by an etch process. Alternatively or additionally,photoresist can also be used to pattern a hard mask (e.g., a siliconnitride hard mask), which, in turn, can be used to pattern an underlyingfilm.

Reference throughout the specification to conventional etchingtechniques known in the art of semiconductor fabrication for selectiveremoval of polysilicon, silicon nitride, silicon dioxide, metals,photoresist, polyimide, or similar materials includes such processes aswet chemical etching, reactive ion (plasma) etching (RIE), washing, wetcleaning, pre-cleaning, spray cleaning, chemical-mechanicalplanarization (CMP) and the like. Specific embodiments are describedherein with reference to examples of such processes. However, thepresent disclosure and the reference to certain deposition techniquesshould not be limited to those described. In some instances, two suchtechniques may be interchangeable. For example, stripping photoresistmay entail immersing a sample in a wet chemical bath or, alternatively,spraying wet chemicals directly onto the sample.

Specific embodiments are described herein with reference toferroelectric capacitors that have been produced; however, the presentdisclosure and the reference to certain materials, dimensions, and thedetails and ordering of processing steps are exemplary and should not belimited to those shown.

FIG. 1A shows a conventional dynamic random access memory (DRAM) cell100, which is well known in the art. The DRAM cell 100 includes atransistor 102 and a storage capacitor C_(s). Multiple DRAM cells 100are typically arranged in a two-dimensional memory array such that eachDRAM cell can be addressed by specifying a bit line 106 (column) and aword line 108 (row) of the array. To read the DRAM cell 100, the bitline 106 can be brought to a voltage that is half of the voltage storedas a logic 1 on a capacitor. The transistor 102 is then turned on byenergizing the word line 108, causing current to flow between thestorage capacitor C_(s) and the bit line 106. If the storage capacitorcontains a logic 1, the voltage V_(c) exceeds the bit line voltageV_(BL), and thus current flows from the storage capacitor to the bitline. If the storage capacitor C_(s) contains a logic 0, V_(c) is lessthan the bit line voltage, so current flows from the bit line to thestorage capacitor C_(s). The voltage on the bit line is then sensed todetermine whether it increased toward a logic 1 or decreased toward alogic zero in order to read the value stored on the capacitor. To writeto the DRAM cell 100, the bit line 106 is used to charge the storagecapacitor C_(s) to the desired value.

FIG. 1B shows a cross section of the DRAM cell 100, in which the storagecapacitor C_(s) is fabricated on a silicon substrate, on top of thetransistor 102. Parts of the storage capacitor C_(s), including thebottom electrode 110, top electrode 112, and dielectric 114, are clearlyshown. In a DRAM, higher capacitance allows for greater storagecapacity. High capacitance, C=κ∈A/d, corresponds to capacitor plateshaving a large surface area, A, and a small spacing, d. On the otherhand, transistor switching speed for operating the memory increases asthe dimensions get smaller. So, there is an inherent conflict betweenthe need for higher speed, which is achieved with smaller dimensions,and the need for larger storage capacity, which is achieved with largersize capacitors. One way to compensate for this, according to the priorart, is to have the capacitors extend vertically above the transistor,as shown in FIG. 1B.

FIG. 2A shows a molecular model of a ferroelectric capacitor 120 asenvisioned by C. S. Hwang of Seoul National University in a presentationentitled “Semiconductor Memory Technology: It Is Time to Shift theParadigm,” presented at the Spring, 2013 meeting of the MaterialsResearch Society, held in San Francisco, Calif. The ferroelectriccapacitor 120 includes a ferroelectric layer 122 and a dielectric layer124, sandwiched between a metallic layer 126, which serves as a lowerelectrode, and an upper electrode 128. The ferroelectric layer 122 ismade of Pb(Zr_(0.2)Ti_(0.8))O₃, or “PZT”, and the dielectric layer 124is made of SrTiO₃. The ferroelectric layer 122 is shown as threemolecules thick, while the metallic layer is shown as two moleculesthick. Together the layers 122 and 124 form a ferroelectric bi-layer. Avoltmeter 125 is shown coupled across the ferroelectric capacitor 120 tomonitor the polarization response.

FIG. 2B shows a circuit schematic 125 that corresponds to theferroelectric capacitor 120. In the circuit schematic 125, the upperelectrode 128 is coupled to a voltage source V_(s) and the metalliclayer 126 is grounded. FIG. 2C shows a polarization curve 130 showingthe electric polarization of the ferroelectric capacitor 120 in responseto application of a voltage. The polarization curve 130 is part of ahysteresis curve that resembles a conventional ferromagnetic hysteresiscurve in certain respects. As the electric field associated with theapplied voltage increases, the electric polarization increasesmonotonically. At 131 and 133, the slope of the polarization curve ispositive, similar to a conventional ferromagnetic hysteresis curve.Unlike a conventional ferromagnetic hysteresis curve, however, a portionof the polarization curve 130 shown within the dashed box 132 exhibits anegative slope 134 that corresponds to a negative capacitance. Inaccordance with the theory set forth by Salahuddin, the polarizationcurve 130 predicts that when such a ferroelectric capacitor 120 havingnegative capacitance is placed in series with a conventional capacitor,the capacitance of the series combination will be very large, despitethe dimensions of the device being very small. By producing such a largecapacitance, the series combination overcomes the scaling limitationsthat have traditionally posed a challenge to DRAM cell development.

FIGS. 3A, 3B, 3C, and 4 are excerpted from Hwang. FIGS. 3A-3C showexperimental data confirming that the theoretically predictedcapacitance behavior is observed for the bi-layer ferroelectriccapacitor 120. FIG. 3A shows a first series of plots 136 of capacitanceas a function of time for a single layer of ferroelectric material,e.g., the layer 122 alone, for comparison with the bi-layer capacitor.The FE in this example is a 150-nm thick layer of PZT. The maximumcapacitance 138 of the FE layer alone in response to a series of appliedcharging current pulses is about 30 nF.

FIG. 3B shows a second series of plots 140 of capacitance as function oftime for a ferroelectric bi-layer, e.g., layers 122 and 124 together,for comparison with the first series of plots 136 shown in FIG. 3A. Theferroelectric bi-layer in this example includes the 150-nm thickferroelectric layer made of PZT, and a 4.5-nm thick dielectric layermade of SiO₂. It is observed that, in response to a series of appliedcharging current pulses, the ferroelectric bi-layer exhibits a transientcapacitance spike 142 to about 375 nF, ten times greater than thetransient response shown in FIG. 3A that is observed for a single layerof 150-nm thick PZT without the SiO₂ layer. The capacitance spike 142thus confirms the behavior predicted by the polarization curve andEquation (3). While the capacitance spike is not infinite, it satisfiesthe prediction because the capacitance spike 142 is so large.

FIG. 3C shows a plot of bi-layer capacitance as a function of thethickness of the SiO₂ dielectric layer. For dielectric layer thicknessesless than 2.0 nm, the transient capacitance observed in response to anapplied current pulse is negative. For thicknesses greater than 2.0 nm,e.g., the case shown in FIG. 3B, the capacitance observed in response toan applied current pulse is positive. Thus, the negative capacitancevalues shown within the circle 144 along the line corresponding topulsed measurements 145 is limited to a range of dielectric thicknesses,as well as being a transient effect, i.e., limited to within a shorttime interval.

FIG. 4 shows a cross-sectional view of an inventive ferroelectric DRAMcell 146 in which the conventional dielectric storage capacitor C_(s)has been replaced with a pair of bi-layer ferroelectric capacitors 120on top of vertical transistors 102. Within the ferroelectric capacitor120 are shown the ferroelectric layer 122, the dielectric layer 124, andelectrodes 126, 128. The ferroelectric capacitor on the right-hand sideis shown overlying a vertical transistor 102 in which a section is cutaway, revealing interior layers of the transistor.

DRAM structures that show details of the vertical transistor 102 aredisclosed in U.S. Pat. Nos. 7,824,982 and 6,734,484. Portions of theferroelectric capacitor 120 of the ferroelectric DRAM cell 146 are shownin FIG. 5 as an inventive integrated structure formed on a semiconductorsubstrate. FIGS. 6-10 below then describe the process of forming anintegrated array of such DRAM cells 146.

With reference to FIG. 5, completed ferroelectric capacitor portions ofthe ferroelectric DRAM cell 146 are shown, including the ferroelectriclayer 122, the dielectric layer 124, and lower, middle, and upperelectrodes 126, 127, and 128, respectively. The lower and middleelectrodes, 126 and 127, provide circuit designers with electricalaccess to positive capacitors C_(p) between adjacent metal lines. Seriescombinations of such positive capacitors yield very small overallcapacitances. Meanwhile, the lower and upper electrodes, 126 and 128,provide electrical access to the very large overall capacitance of theFE/dielectric series combination. A deep filled trench 148 provideslateral separation between the two capacitors 120.

With reference to FIGS. 6-10, fabrication of one embodiment of an arrayof ferroelectric DRAM cells 146 according to an exemplary method 150 isshown and described. FIG. 6 shows a high level sequence of steps in theexemplary method 150. FIGS. 7-10 illustrate formation of theferroelectric capacitor portions of the ferroelectric DRAM cells 146,step-by-step, following the exemplary method 150. In this embodiment,positive and negative capacitors C_(p) and C_(n) are incorporated intoan interconnect structure so as to influence operating characteristicsof the interconnect structure, for example, RC delays and the like.

At 152, vertical transistors 102 are formed on a semiconductor substrateaccording to methods that are well known in the art, for example, asdescribed in U.S. Pat. Nos. 7,824,982 and 6,734,484.

At 154, an array of positive capacitors C_(p) is formed on thesubstrate, including bottom electrodes 126, the dielectric layer 124,and middle electrodes 127.

At 156, an array of negative capacitors C_(n) is formed on thesubstrate, including the ferroelectric layer 122 and upper electrodes128. In the embodiment shown and described, the ferroelectric layer 122is a ferroelectric film stack that includes three sub-layers, 122 a, 122b, and 122 c, each sub-layer made of a different ferroelectric material.

At 158, the deep filled trenches 148 are formed as separators betweenadjacent pairs of capacitors.

FIG. 7 shows the formation of a positive capacitor C_(p) at 154,according to one embodiment. The positive capacitor C_(p) includes thebottom electrodes 126, the middle electrodes 127, and the dielectriclayer 124. First, a thin layer of dielectric material is formed on thesubstrate using a standard deposition process such as CVD, PVD, or thelike. The thin dielectric layer is preferably about 10 nm thick butcould be up to about 60 nm thick. The thin dielectric layer is made ofsilicon dioxide (SiO₂), for example, or any ultra-low-k dielectricmaterial having a dielectric constant within the range of about 1.5-3.0.

Following deposition, an array of bottom electrodes 126 is formed in thethin layer of dielectric material using a damascene process. The thinlayer of dielectric material is patterned using a photoresist mask or ahard mask, and openings are etched in a conventional way. The width ofthe openings is desirably within the range of 1-20 nm. The openings arethen filled with an interconnect metal, for example, a metal liner madeof titanium (Ti), or titanium nitride (TiN), or tantalum nitride (TaN)followed by a bulk metal such as tungsten (W), copper (Cu), or aluminum(Al). If the bulk metal is copper, then the metal liner used may be TaN,for example. If the bulk metal is not copper, the metal liner used maybe Ti or TiN, as other examples. The interconnect metal is then polishedback to the level of the dielectric layer using a CMP process, therebycreating a structure having a substantially planar surface.

A thick layer of dielectric material is then deposited over the array ofbottom electrodes. The thickness of the thick dielectric layer isdesirably within the range of about 20-40 nm. The dielectric layer 124includes the thick layer and the original thin layer of dielectricmaterial. The two layers within the dielectric layer 124 are desirablymade of the same material. However, this is not required. For example,the thin layer may be made of a silicon dioxide material while the thicklayer is made of silicon nitride.

An array of middle electrodes 127 is then formed in the dielectric layer124, again using a damascene process similar to that used to form thearray of bottom electrodes described above. The array of middleelectrodes 127 is similar to the array of bottom electrodes 126, againpresenting a substantially planar surface to the next layer that will beformed on top of the inlaid middle electrodes.

FIG. 8 shows the formation of the negative capacitor C_(n) at 156,according to one embodiment. The negative capacitor C_(n) includes theupper electrodes 128 and the ferroelectric film stack sub-layers 122 a,122 b, and 122 c, and shares the middle electrodes 127 with the positivecapacitor C_(p). First, a first layer of ferroelectric material 122 a isformed on the substrate. In one embodiment, the first layer offerroelectric material 122 a is 1-20 nm of strontium ruthanate, alsoknown as SRO (SrRuO₃). Next, a second layer of ferroelectric material122 b is formed on the substrate. In one embodiment, the second layer offerroelectric material 122 b is 1-20 nm of strontium titanate (SrTiO₃).Next, a third layer of ferroelectric material 122 c is formed on thesubstrate. In one embodiment, the third layer of ferroelectric material122 c is 1-20 nm of lead zirconate titanate, also known as PZT((Pb(Zr_(0.2)Ti_(0.3))O₃). Alternatively, the third layer offerroelectric material 122 c can include BaTiO₃ or PbTiO₃. Depositionmethods for ferroelectric materials are currently under development andmany are available in the market today. More will be developed in thefuture. Any such methods that are appropriate and effective can be usedto deposit any of the ferroelectric materials described herein, for thepurposes of forming the ferroelectric layer 122. Such methods include,but are not limited to, CVD, PVD, sputtering deposition, electrophoreticdeposition (EPD), and chemical solution deposition (CSD). An embodimentmay also include barrier layers at least partially surrounding theferroelectric materials, and/or intervening between a givenferroelectric material and another material, to prevent shorts formingthrough adjacent dielectric materials, and to sufficiently contain theferroelectric materials.

An array of upper electrodes 128 is formed in the third layer offerroelectric material 122 c, again using a damascene process similar tothat used to form the arrays of bottom and middle electrodes 126 and127, respectively, as described above. The size and materials of thearray of upper electrodes 128 are similar to those of the arrays ofbottom and middle electrodes 126.

FIG. 9 shows the formation, at 158, of the array of the deep filledtrenches 148, according to one embodiment. Deep trenches are etchedthrough all of the layers, down to the substrate, using, for example, ahigh power anisotropic etch process which is well known in the art asbeing suitable for etching vias. The dimensions of the trenches willdetermine, in part, the inter-trench capacitance and trench resistance.The trenches are then filled, first with two conformal liners, and thenwith bulk metal. The first trench liner is an insulator such as, forexample, silicon carbide (SiC). The second trench liner and the bulkmetal are the standard metal liner and bulk metals which are also usedin forming the metal electrodes 126, 127, and 128. The trench fillmaterials are then polished back to be coplanar with the third layer offerroelectric material 122 c.

FIG. 10 shows a second, alternative embodiment of the completed array ofcapacitors, in which the ferroelectric layer 122 is formed first, andthe dielectric layer 124 is formed on top of the ferroelectric layer122.

FIG. 11 shows a third, alternative embodiment of the completed array ofcapacitors, which excludes the metal electrodes 126, 127, and 128. Thearray shown in FIG. 11 serves as a high density, high performance metalinterconnect structure, with negligible RC delays. Structuralcompensation for the lack of electrodes can be made by using a ULKdielectric 124 that has a high dielectric constant, about 4.0. Such aULK dielectric 124 provides enhanced structural stability duringformation of the array, especially prior to completion of the deepfilled trenches 148. Total capacitance between adjacent metal lines(i.e., the deep filled trenches 148) used as interconnects can be tunedto approximately zero by designing C_(n) and C_(p) to have substantiallyequal capacitance values, C_(n)=−C_(p), so they cancel out one another.

The various embodiments described above can be combined to providefurther embodiments. All of the U.S. patents, U.S. patent applicationpublications, U.S. patent applications, foreign patents, foreign patentapplications and non-patent publications referred to in thisspecification and/or listed in the Application Data Sheet areincorporated herein by reference, in their entirety. Aspects of theembodiments can be modified, if necessary to employ concepts of thevarious patents, applications and publications to provide yet furtherembodiments.

It will be appreciated that, although specific embodiments of thepresent disclosure are described herein for purposes of illustration,various modifications may be made without departing from the spirit andscope of the present disclosure. Accordingly, the present disclosure isnot limited except as by the appended claims.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

The invention claimed is:
 1. An interconnect structure, comprising: acapacitive structure configured to store data for a memory cell, thecapacitive structure including, a ferroelectric capacitor includingconductive plates and exhibiting a negative capacitance, theferroelectric capacitor formed on a semiconductor substrate; adielectric capacitor including an ultra-low-k dielectric formed betweenconductive plates, the dielectric capacitor electrically coupled inseries with the ferroelectric capacitor; and a plurality of conductivelines formed by the conductive plates of the ferroelectric anddielectric capacitors, the plurality of conductive lines including afirst pair of conductive lines including the conductive plates of thedielectric capacitor and having a first capacitance between the firstpair of conductive lines, and the plurality of conducive lines includinga second pair of conductive lines including the conductive plates of theferroelectric capacitor and the dielectric capacitor and having a secondcapacitance between the second pair that is greater than the firstcapacitance.
 2. The structure of claim 1 wherein the ferroelectriccapacitor includes one or more of BaTiO₃, PbTiO₃, andPb(Zr_(x)Ti_(y))O₃.
 3. The structure of claim 1 wherein theferroelectric capacitor includes a ferroelectric material, a conductor,and a dielectric disposed between two conducting plates.
 4. Thestructure of claim 3 wherein the dielectric is made of SrTiO₃.
 5. Thestructure of claim 3 wherein the conductor is made of SrRuO₃.
 6. Thestructure of claim 1 wherein the ferroelectric capacitor includes adielectric/ferroelectric bilayer in which a dielectric material isformed in contact with a ferroelectric material.
 7. The structure ofclaim 1 wherein the interconnect structure is part of a microelectronicmemory cell.
 8. The structure of claim 1 wherein the ferroelectriccapacitor and the dielectric capacitor include a pair of deep trenchesfilled with metal.
 9. A high capacity integrated circuit memory cell,comprising: a transistor; a capacitor structure coupled to thetransistor, the capacitor structure configured to store data for thememory cell and including, first, second, and third parallel conductingplates, the third parallel conductive plate being positioned between thefirst and second parallel conducting plates; a ferroelectric layerformed between and in contact with the first and third parallelconducting plates to form a negative capacitor including the first andthird parallel conducting plates and the ferroelectric layer; and anultra-low-k dielectric layer formed between and in contact with thesecond and third conducting plates to form a positive capacitorincluding the second and third parallel conducting plates and theultra-low-k dielectric layer, the positive capacitor electricallyconnected in series with the negative capacitor to form the capacitivestructure.
 10. The memory cell of claim 9 wherein the capacitivestructure behaves as a stable series combination of dielectric andferroelectric capacitors in response to a voltage applied to the firstand second parallel conducting plates.
 11. The memory cell of claim 9,wherein the ferroelectric layer comprises a ferroelectric stack.
 12. Thememory cell of claim 9, ferroelectric stack comprises sub-layersincluding one or more of BaTiO₃, PbTiO₃, or Pb(Zr_(x)Ti_(y))O₃.
 13. Anarray, comprising: two or more ferroelectric memory cells arranged in aninterconnect structure, each ferroelectric memory cell containing abi-layer ferroelectric capacitor configured to store data for theferroelectric memory cell, the bi-layer ferroelectric capacitorincluding, a first electrode, a second electrode, and a shared electrodepositioned between the first and second electrodes; a ferroelectriclayer positioned between and in contact with the first and sharedelectrodes to form a negative capacitor including the first and sharedelectrodes and the ferroelectric layer; and an ultra-low-k dielectricmaterial positioned between and in contact with the second and sharedelectrodes to form a positive capacitor including the second and sharedelectrodes and the ultra-low-k dielectric material, the positivecapacitor being electrically connected in series with the negativecapacitor to form the bi-layer ferroelectric capacitor.
 14. The array ofclaim 13 wherein the ferroelectric memory cells of the array compriseDRAM memory cells.
 15. The array of claim 13 wherein the ferroelectriclayer of the negative capacitor includes a ferroelectric film stack. 16.The array of claim 15 wherein the ferroelectric film stack includes afirst ferroelectric sub-layer formed on the shared electrode, a secondferroelectric sub-layer formed on the first ferroelectric sub-layer, anda third ferroelectric sub-layer formed on the second ferroelectricsub-layer and in contact with the first electrode.
 17. The array ofclaim 16 wherein the first, second, and third ferroelectric sub-layersinclude one or more of BaTiO₃, PbTiO₃, or Pb(Zr_(x)Ti_(y))O₃.
 18. Thearray of claim 17 wherein the second ferroelectric sub-layer is made ofSrTiO₃.
 19. The array of claim 18 wherein the first ferroelectricsub-layer is made of SrRuO₃.
 20. The array of claim 18, wherein thearray further includes deep trenches filled with metal positionedbetween adjacent ones of the two or more ferroelectric memory cells. 21.An array of memory cells, comprising: a semiconductor substrate; aplurality of transistors formed over the semiconductor substrate; and aplurality of memory cells formed over the plurality of transistors, eachof the plurality of memory cells including at least one of the pluralityof transistors and a capacitive structure including a series-connectedferroelectric capacitor having a negative capacitance and dielectriccapacitor having a positive capacitance are configured to store data forthe memory cell, the series-connected ferroelectric and dielectriccapacitors including first, second, and third parallel conducting platesformed over the plurality of transistors, the first parallel conductingplate being formed over the substrate, the second parallel conductingplate being formed over the first parallel conducting plate, and thethird parallel conducting plate being formed over the second parallelconducting plate, the ferroelectric capacitor including a ferroelectricmaterial formed between the first and third parallel conducting platesto provide the negative capacitance and the dielectric capacitorincluding an ultra-low-k dielectric material formed between the secondand third parallel conducting plates to provide the positive capacitanceof form the series-connected ferroelectric and dielectric capacitorsbetween the first and third electrodes.
 22. The array of claim 21wherein each memory cell includes one of the plurality of transistorsand is a DRAM memory cell.
 23. The array of claim 21, further comprisingdeep filled trenches that separate adjacent ones of the capacitivestructures.